Caustic regeneration



1965 w. K. ROBBINS ETAL 3,216,796

GAUSTIC REGENERATION Filed July 28, 1961 ACID-FREE CATALYTIC HEATING OILFIG.

MERGAPTANS AND WATER ORGANIC ACID EM P E III 8 L 0 C 4 TEMP. CONTROL I20i E EvAPoRAToR STEAM GONDENSATE NAOH BLEED CATALYTIC HEATING OIL MAKE-UPNAOH FIG. 3.

FIG. 2.

INVENTORS. WILLIAM K. ROBBINS JAMES o. SCOTT,

BY 2% My ATTORNEY.

United States Patent Ofi .ice

3,215,796 Patented Nov. 9, 1965 3,216,796 CAUSTIC REGENERATION WilliamK. Robbins and James 0. Scott, Baytown, Tex.,

assignors, by mesne assignments, to Esso Research and EngineeringCompany, Elizabeth, N.J., a corporation of Delaware Filed July 28, 1961,er. No. 127,527 1 Claim. (Cl. 23-184) The present invention relates tothe reconcentration and regeneration of solutions of alkali metalhydroxides which have been used to remove organic acids and mercaptansfrom flowing hydrocarbon streams. More particularly, the presentinvention relates to a method and means for concurrently concentratingthe caustic solution while utilizing the steam evolved duringconcentration to strip mercaptans from the solution. In its morespecific aspect, the present invention relates to a means and method ofregenerating a sodium hydroxide solution which contains dissolvedorganic acids by concentrating and removing mercaptans from saidsolution in a first stage and recovering organic acids from saidsolution in a second stage.

Hydrocarbon streams boiling between about 100 F. and about 800 F. andcontaining mercaptans and organic acids (including phenols andcarboxylic acids) are unsuitable for commercial use because of thecorrosivity of the dissolved contaminants. As a consequence of thiscorrosivity, the product streams must be treated either to remove or toneutralize the effect of these contaminants. One method of removing thecontaminants is by contacting the hydrocarbon stream with a concentratedsolution of the hydroxide of an alkali metal hydroxide such as sodium,potassium or lithium. The use of these hydroxides is effective inremoving the mercaptans, phenols, carboxylic acids and other acidiccontaminants from the flowing stream, but are expensive both in the costof the treating solution as well as in the costs of disposing of thewaste liquid after the caustic solution has become spent. By thepractice of the present invention, the etfective life of such a causticsolution may be extended to a period of several times that experiencedin the manner hitherto utilized. Further, by the practice of the presentinvention, it has been found that although the caustic solutions whichare used in the practice of the present invention are highly viscous,concentrations of the caustic to the desired gravity may be accomplishedat atmospheric pressure. Hitherto it has been considered necessary inreconstituting these highly viscous solutions to use a vacuumevaporation system in order to minimize effects of slugging and bubblingwithin the evaporator. It has further been found by the practice of thepresent invention, that the steam evolved during the reconcentration orevaporation step may be utilized to strip mercaptans from the solution,thereby obviating the preliminary removal of mercaptans beforereconstitution.

During the contacting of the flowing hydrocarbon stream with the causticsolution, the water which normally occurs in the flowing hydrocarbonstream is also removed along with the contaminants sought to be absorbedby the caustic scrubbing solution. The natural result of the absorbingof this moisture is a constant dilution of the scrubbing caustic. If thecaustic solution is maintained at a gravity above 42 Baum, the organicacids extracted from the hydrocarbon stream may be separated into asupernatant layer by cooling the caustic to a temperature of about 100F. to 150 F., but when the caustic strength falls below 42 Baum,particularly where the caustic strength is below 40 Baum, the organicacids are completely soluble in the caustic and will not form theseparate layer. Therefore, they cannot be decanted from the caustic tankand an organic acid buildup occurs which causes the caustic to becomeunusable and spent in a relatively short time. The caustic strength istherefore preferably maintained within a range of about 42 to 50 Baum.

The present invention prevents the buildup of organic acids byreconstituting the caustic solution to the desired gravity. Moreover,the practice of the present invention prevents a buildup of mercaptanswithin the caustic solution which also would result in an untimelydeactivation of the caustic solution.

The practice of the present invention may be more particularlyunderstood by a reference to the appended drawings wherein:

FIG. 1 is a general schematic diagram of the scrubbing system;

FIG. 2 is a representation of a particular feed nozzle into theevaporator;

FIG. 3 is a plan view of the nozzle taken on lines 33 of FIG. 2; and

FIG. 4 is a sectional elevation of the nozzle taken on line 4-4 of FIG.3.

Referring more particularly to FIG. 1, the practice of the presentinvention relates to the treatment of catalytic heating oil, forexample, which is introduced into a scrubber by way of line 102 and isdischarged after contacting with the caustic solution by way of line104. A scrubbing caustic solution, such as sodium hydroxide, isintroduced into the scrubbing tower by way of line 106 and is passeddownwardly through the tower in contact with the flowing hydrocarbonstream to be discharged at the bottom of the tower by way of line 108.During the passage through the scrubbing tower, the caustic solutionabsorbs the mercaptans, phenols, carboxylic acids, other aromatic andparaflinic acids, and water, which are present in the catalytic heatingoil feed stock. Therefore, the caustic solution passed by way of line108 is contaminated with the absorbed acidic and sulfur-containingcompounds as well as being diluted to a gravity somewhat below theoptimum.

The solution is then charged by Way of line 108 into an evaporator 110and is passed into the shell 112 of the evaporator in a distributed formby means of a bafile 114 which is arranged above the inlet so that thematerial charged into the evaporator impinges upon the bafile and iswell distributed. It should be apparent from FIG. 1 that the solution isnot contacted with air during the heating step within evaporator 110,and is not contacted with air anywhere in the closed circulation system.The evaporator 110 provides a plurality of tubes 116, each of whichdefines a vertically disposed, elongated heating zone having a crosssection which is small relative to the elongation thereof. Thedistributed caustic feed is then passed through a series of tubes 116and is discharged by way of line 118. During passage through tubes 116,the caustic is heated to a temperature of 215 F. to 300 F. by means ofsteam which is introduced by way of line 120 controlled by valve 122 andpasses through the steam jacket within the shell 112 to be discharged byway of line 124 as condensate. The caustic soda is maintained within theevaporator at a temperature of about 215 F. to 300 F. for a time periodsufiicient to evaporate enough water to concentrate the solution fromthe operating gravity of about 40 to 43 Baum to a gravity of about 45Baum or higher, preferably about 44 to 48 Baum. Also, the time periodshould be suflicient to allow the mercaptans to be stripped from thecaustic solution and carried into the vapor phase with the evolvedsteam.

The total efiiuent, liquid, gas and vapor, from the evaporator 110 ispassed by way of line 118 into a first separator 126 wherein thevaporous steam and gaseous mercaptans are allowed to pas overhead by wayof line 128 through condenser 130 for disposal. The liquid is passedfrom the separator by way of standpipe 132 and line 134 into pump 136,and is discharged from pump 136 by way of line 138, valve 140, andcooler 142 into a second separator 144, from whence an organic acidsuprenatant layer is withdrawn by way of line 146 and a reconstitutedand regenerated caustic soda solution is discharged by way of line 148for recycle by way of line 150 into line 106 and into the scrubber 100.The caustic may be discharged intermittently or continuously by way ofthe caustic bleed line 152, while makeup caustic of 45 to 50 Baum orhigher is introduced in offsetting amounts through line 154.

Returning now to the evaporator system proper, it is seen that a line156 interconnect the discharge line 134 from the first separator and theevaporator 110. This line 156 recirculates a portion of the caustic tothe evaporator to assure a complete concentration of the caustic andremoval of the mercaptan. The evaporator 110 is provided with an inlet158 for this recycle stream, and the inlet 158 is further provided withan orifice plate or choke plate 160 which provides sufiicient pressuredrop to prevent the passage of a portion of the feed which is introducedby way of line 108 into the line 156 to bypass the evaporation system.The orifice should be about 1% to of the area of the return conduit. Itshould be understood that the recycle stream being recharged into theevaporator 110 may be provided with suitable pumping means if necessaryto provide sufficient head for the recirculation rate desired.Preferably, however, the recycle is accomplished by relying on thepressure head differential which may be obtained by mounting theseparator 126 at a slightly higher elevation than the evaporator 110,and allowing the evolved steam within the tubes 116 to provide a vaporlift for the solution into the separator 126.

Referring now to FIG. 2, a particular form of injection nozzle isdisclosed which obviates the necessity of using a choke plate such asthe plate 160 shown in FIG. 1. In the modification of FIG. 2, a feednozzle 200 is shown within an evaporator 210 which is generally similarto that shown in FIG. 1. The recycle inlet 220 shown in FIG. 2 is freeof obstruction, and need not be provided with a choke plate. This isaccomplished by mounting the feed nozzle 200 at a position at least ashigh as the bottom of the recycle inlet pipe, but preferably above thisposition, and in forming the feed nozzle with a generally hemisphericalupper surface with discharge passages extending radially therethrough sothat the feed stream will be directed above the inlet 220.

The structure of the nozzle 200 may better be understood by referring toFIGS. 3 and 4 wherein there is disclosed a plan view and a sectionalelevational view of the nozzle. In particular, referring to FIG. 4, thenozzle 200 is seen to communicate with the feed pipe 240 which containsthe charge stream. Radial passages 250 are formed in the head of thenozzle for directing the feed stream in a direction above the horizontalplane defined by the lower portion of the nozzle indicated by thenumeral 260. Therefore, with the nozzle mounted above the recycle pipe,the vector forces imported to the feed stream will prevent the freshfeed stock from entering the recycle nozzle.

By the practice of the present invention, caustic consumption has beenreduced over 50%. In the practice of caustic scrubbing of a catalyticheating oil stream without regeneration, an average life span of acaustic solution charged had been established at about five days. By

utilizing the present invention, the life span of the caustic has beenextended to about 21 days. This increase in life of over four times thatpreviously experienced indicates the importance and the effectiveness ofthe present invention. As a further description of the benefits of thepresent invention, the following examples are set forth.

Example I Catalytic heating oil (30,000 bbls./day) was passed through acaustic scrubber in contact with a total charge of 1,000,000 lbs. of 50Baum sodium hydroxide solution (circulated at a rate of 2% to 5% byvolume-dilution from water in feed decreasing the Baum gravity). Thecaustic was recirculated until the specific gravity reached 40 Baum, atwhich time the caustic was discarded and a new caustic charge of 50 Baumspecific gravity was injected into the system. Under these conditions,the caustic consumption of 50 Baum sodium hydroxide was about 2,000bbls. or 520,000 l bs/month.

Example II Utilizing the evaporator system as described in FIG. 1, thecatalytic heating oil (30,000 bbls./day) was passed in contact with atotal charge of 1,000,000 lbs. of caustic soda which was circulated at2% to 5% by volume. The caustic soda solution was reconstituted as setforth in the discussion of the aforesaid figure with mercaptans andorganic acids being removed in accordance with the invention.

By utilizing the practice of the present invention, the causticconsumption is about 800 to 900 bbls./month of 50 Baum caustic orslightly less than 235,000 lbs./ month, less than 50% of the causticconsumption heretofore experienced. Also, during the operation of theevaporator system, 95,000 lbs. of marketable organic acids wererecovered in a months operation.

As may 'be seen by comparison of Examples I and II above, besides therecovery of marketable by-product organic acids, the caustic consumptionhas been reduced over 50%. In the practice of the present invention, thesteam consumption on a monthly basis is about 7,000 to 12,000 lbs./hr.(estimated average is 8,000 lbs/hr.) of steam, which results in a high,attractive economic advantage based on the saving of caustic solution.An added advantage is the lessening of spent caustic solution which mustbe disposed of.

The nature and practice of the present invention having been set forthin detail, including a preferred manner and best mode of practicing theinvention, what is desired to be protected by Letters Patent should bedetermined only by the appended claim and should not be limited by thespecific examples hereinabove given.

We claim:

A method for regenerating a sodium hydroxide solution having a gravityless than 42 Baum and containing dissolved mercaptans and organic acidswhich comprises the following steps in sequence:

in the absence of air indirectly heating said solution in at least onevertically disposed, elongated heating zone having a cross section whichis small relative to the elongation thereof,

to a temperature of about 215 F. to 300 F.,

for a time sufficient to concentrate said solution to a gravity of atleast 42 Baum,

while evolving steam generated solely from the solution and mercaptansin the vapor phase,

the evolved steam being the only source of stripping steam for removingmercaptans from said solution,

separating said evolved steam and mercaptans in the vapor phase fromsaid solution,

cooling said solution to a temperature from F. to

whereby said organic acids form a supernatant layer,

and separating said organic acid from said solution,

whereby said sodium hydroxide solution is rendered ered.

References Cited by the Examiner UNITED STATES PATENTS Smith 23260Fleming et a1. 23-260 Hewlett 23184 Payne et a1./ 23-1-84 6 Harper et a1208235 Gleim et a1 2082'35 Hainsworth 23184 Urban 208235 Childs 23184Thomas 23-184 Shirley et a1. 23-185 MAURICE A. BRINDISI, PrimaryExaminer.

Pye 23 1, 4 10 ALPHONSO D. SULLIVAN, Examiner.

